Researchers finally reveal how birds get their colour

6:52 AM, 9th August 2017

A representative image of a colourful bird.

CHICAGO, US: Birds' feathers or plumage, are some of the most amazing variable animal characteristics that can be observed by the naked eye. The patterns that we see in birds' feathers are made up of complex combinations of mottles, scales, bars, and spots. But, how are these colours and patterns made?

Dr Ismael Galvan and his expert research team from the University of Chicago, US studied the plumage coloration in 9,000 bird species to see what types of pigments were present in its complex feather patterns.

Plumage coloration mainly happens courtesy of two types of pigments: melanins, which produce a range of black, grey, brown, and orange colours, and carotenoids, which are used by specialized feather structures to generate brighter colour hues.

The study is published in the journal Physiological and Biochemical Zoology.

Birds cannot produce carotenoids on their own. For feathers with bright colours, birds must consume food items that contain these pigments, and the carotenoids circulate through the bloodstream and to the feather follicles. Birds' bodies do not have direct cellular control of synthesizing and depositing carotenoids; nor do they have control of the specialized feather structures, which react to the consumed carotenoids with a mechanism that is not regulated by specialized cells.

Melanins, on the other hand (or should that be on the other wing), are synthesized by in the birds' bodies in special cells called "melanocytes," which work together with feather follicles to achieve a fine control of pigmentation. Although studies frequently focus on carotenoids in bird coloration,

"Knowing before that different pigments and structures produce different types of colours in feathers, we examined the appearance of the plumage of all species of extant birds and determined if the colour patches that they contain are produced by melanins or by other pigmentary elements. We also identified those plumage patterns that can be considered complex, defining them as those formed by combinations of two or more discernible colours that occur more than two times uninterruptedly through the plumage," said Galvan.

This study was very large in scope with the goal of supporting a general conclusion for all birds, to finally answer the question of how birds develop colourful and detailed patterns.

The team found that about 32 percent of the species studied have complex plumage patterns, with the vast majority of these complex patterns produced by melanins rather than carotenoids. Metaphorically, if the birds were artists, they would use carotenoids as a broad brush to produce colour patches, with melanins as a detail paint brush to produce more intricate designs.

A few birds are exceptions to this rule: Three bird families do have complex plumage patterns without melanins. Fruit doves, cotingas and one type of stork have unusual colours that appear to be produced by their bodies making metabolic modifications to the carotenoid pigments that they consume.